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Book. _J j - • 



„_7. Issued February 17, 1816. 

U. S. DEPARTMENT OF AGRICULTURE, 
^BUREAU OF ANIMAL INDUSTRY. 



CHEMICAL TESTING OF MILK 
AND CREAM 



BY 



ROSCOE H. SHAW, 

Chemist, Dairy Division. 




WASHINGTON: 

GOVERNMENT PRINTING OFFICE, 

1916. 



6 



\V 



D. of D. 
WAR 17 1916 






A. -7. Issued February 17, 1916. 

U. S. DEPARTMENT OF AGRICULTURE, 
BUREAU OF ANIMAL INDUSTRY. 

A. D. MEL VEST, Chief. 



CHEMICAL TESTING OF MILK AND 
CREAM. 1 



By Roscoe H. Shaw, Chemist, Dairy Division. 



CONTENTS. 



Chemical nature of milk 1 

Testing for fat 3 

Determination of total solids in milk 22 

Determination of specific gravity of milk 26 

Calculating total solids by formula 28 

Determination of acidity of milk and cream 32 

The detection of preservatives 34 

Chemicals and apparatus used in the chemical analysis of milk 

and cream 36 



CHEMICAL NATURE OF MILK. 

In order to follow intelligently the methods for testing 
milk and cream some knowledge of the chemistry of milk 
is essential. From a chemical standpoint milk is a very 
complex substance. The component parts may, however, 

1 In preparing this, bulletin free use has been made of the various 
publications on the subject, particularly "Testing Milk and Its Pro- 
ducts," by Farrington, E. H., and Woll, F. "W. (Madison, Wis., 1911), 
and " Modern Methods of Testing Milk and Its Products," by L. L. 
Van Slyke (New York, 1907). 
15037°— 16 1 



be classified into a few well-marked groups, as follows: 
(1) Water, (2) fat, (3) nitrogenous constituents, (4) sugar, 
and (5) ash. The components other than water are col- 
lectively known as total solids or milk solids, and the 
solids other than fat as solids not fat. Milk serum, or 
more properly milk plasma, is the term used to denote 
the milk minus the fat; hence the terms serum solids and 
plasma solids are synonymous with solids not fat. 

Water. — The water in milk varies from 82 to 90 per 
cent. The usual variation in mixed-herd milk is much 
less and is probably covered by 84 to 88 per cent. 

Fat. — The fat in milk — milk fat or butter fat — is not in 
solution but exists as an emulsion of microscopic globules 
so small that a single drop of average milk contains more 
than one hundred millions of them. These globules, even 
in milk from one cow, are not all of the same size. Some 
may be two or three times the size of others, the average 
size depending upon several factors, the principal one of 
which is the breed of the animal. Chemically the fat is 
not a single compound but a mixture of several compounds 
known as glycerids. Some of these glycerids are common 
to all fats, while others are peculiar to butter. This fact 
is made use of in detecting oleomargarin or artificial 
butter. 

Cows' milk usually contains from 3 to 6 per cent of fat, 
depending very largely upon the breed of the animal. 

Nitrogenous constituents. — These are principally casein 
and albumin, with traces of less important nitrogenous 
compounds. The coagulum produced by rennet, dilute 
acids, or certain other chemicals, when added to milk, is 
chiefly casein. Albumin is the flocculent precipitate 
produced by heating whey or skimmed milk from which 
the casein has been removed. In constitution and be- 
havior it closely resembles white of egg. Casein is not 
really in solution in the milk, but exists in an extremely 
fine colloidal condition in combination with some of the 
ash constituents. With an appropriate filter of clay it 
is possible to separate it from the water. Albumin is in 
true solution in the water of the milk. Frequently, but 
improperly, the term casein is applied to all the nitrogen- 
ous constituents in milk. Sometimes the term total pro- 
teins is used in referring to the nitrogenous constituents 



taken as a whole. The amount of casein in average 
cows' milk varies from 2 to 4 per cent and the albumin 
from 0.5 to 0.8 per cent. 

• Sugar. — Milk sugar, or lactose, belongs to a group 
known as carbohydrates, and is a white substance less 
sweet in taste than cane sugar. Milk sugar is broken up 
into lactic acid by the action of bacteria, this bringing 
about the souring of milk. Milk sugar is in solution in 
the water of the milk and is present to the extent of from 
3.5 to 6 per cent. 

Ash. — The ash, or the mineral part of milk, exists to 
the amount of about 0.75 per cent and consists largely 
of the chlorids and phosphates of sodium, potassium, 
magnesium, and calcium. 

AVERAGE CHEMICAL COMPOSITION. 

The table below gives the average of more than 5,000 
analyses of milk at the New Vork State Agricultural Exper- 
iment Station, Geneva: 

Per cent. 

Water 87. 1 

Total solids 12. 9 

Fat : 3.9 

Casein 2.5 

Albumin 7 

Sugar 5. 1 

Ash 7 

TESTING FOR FAT. 

In the following remarks on the testing of milk and 
cream the aim will be to present the subject in such a man- 
ner that it may be followed by those who have had neither 
chemical-training nor a course of any sort in milk testing. 
To those who have had such training the following pages 
will doubtless appear very elementary and overburdened 
with detail. 

TESTING MILK FOR FAT. 

Preparing the sample for testing. — As before mentioned, 
fat is not in solution in milk, but is in an emulsion of very 
fine globules. These, being lighter than the surrounding 
serum, tend to rise, carrying with them some of the other 
solids, resulting in the familiar creaming of milk. Before 



the test can be made a homogeneous mixture must be ob- 
tained. This can best be obtained by pouring the milk 
several times from one vessel into another. When the 
sample is small, beakers are convenient for this purpose, 
and if the sample has not remained in the container more 
than a few hours, pouring back and forth four or five times 
is sufficient. When, however, the sample has stood for 
some time in the container, the cream layer is liable to be 
hard and to adhere to the walls. This is particularly true of 
preserved samples. In such event it is well to place the 
container in warm water until the cream has become soft- 
ened and can then be easily removed. Care must be taken 
that none of the cream is left on the cover of the container ; 
if, however, any is left, a brush such as is used in cleaning 
beakers is useful in dislodging it. 

The sample must always be well mixed immediately 
before measuring out a charge for testing. If several 
charges are to be measured out, the sample must be mixed 
each time. Thorough mixing is imperative for accurate 
work. 

Partially churned milk. — Milk from some cows, notably 
of the Jersey breed, churns very easily and sometimes a too 
vigorous agitation in the mixing of such milk results in 
some of the fat collecting in small granules which refuse to 
emulsify again. This also frequently happens when the 
milk is sent a long distance in partially filled containers. 
These granules are easily recognized, and when they are 
present special treatment is required to prepare the sample 
for testing. A little ether equal in volume to 5 per cent 
of the milk may be added, and the container stoppered and 
vigorously shaken. The ether will dissolve the granules 
and the solution will mix with the milk. A fairly accurate 
charge may now be quickly removed, but the percentage 
obtained must be corrected for the volume occupied by the 
ether. 

Another and perhaps a better way to treat churned milk 
is to place the container in hot water until the milk has 
attained a temperature of about 110° F. In a few minutes 
at this temperature the granules will have melted. The 
container is then vigorously agitated and a charge for test 
immediately measured out. 



The partial churning of the sample is not a frequent 
occurrence and with proper care can always be avoided. 
When samples are to be sent a considerable distance the 
containers should be completely filled so that no space is 
left at the top . A good way is to fill a bottle to overflowing 
with the mixed sample and then to insert a rubber or cork 
stopper having a hole about one-eighth of an inch in diame- 
ter. As the stopper goes to its place the milk will spurt out 
through the hole; the hole is then filled with a piece of 
glass rod or a wooden plug. When treated in such a man- 
ner milk will not churn. 

Sour milk. — While the souring of milk does not affect 
the fat, it is impossible to obtain a representative charge 
from curdled milk without special treatment. , In order to 
obtain a good mixture it is necessary to dissolve the curd. 
This may be accomplished by adding 5 or 10 per cent by 
volume of a strong solution of either caustic soda or potash; 
strong ammonia water may also be used. The alkali must 
be thoroughly mixed with the milk until it is completely 
liquid. The charge for test must be immediately meas- 
ured out and a correction made in the final percentage for 
the volume occupied by the alkali solution. If desired, 
the powdered alkali may be added directly to the milk in 
small portions at a time, being sure that one portion is 
dissolved before another is added, and agitating until the 
milk has become liquid. No correction is necessary for 
the volume occupied by the powdered lye. When making 
a fat test on milk containing alkali, special precautions 
must be observed in adding the sulphuric acid, as an 
excessive amount of heat is generated and the contents of 
the test bottle may be thrown out. When alkali is used, 
slightly more acid is required. 

THE BABCOCK TEST. 

The Babcock test for fat in dairy products, named for its 
inventor, Dr. S. M. Babcock, chief chemist of the Wiscon- 
sin agricultural experiment station, is based upon the 
fact that strong ,sulphuric acid will dissolve the serum 
solids in milk and set the fat free from its emulsion. In 
conducting the test, the charge is placed in a specially 
constructed test bottle and mixed with the proper quan- 



tity of sulphuric acid. The acid performs other functions 
than the simple solution of the serum solids. Much heat 
is developed by its action, and this causes the fat globules 
to lose their individuality and run together, a condition 
which greatly facilitates the separation from the serum, 
and this separation is still further accelerated by the 
increase in specific gravity of the serum caused by the 




f 5 ? 



Fig. 1.— Old type of 
Babcock milk-test 
bottle. 



Fig. 2.— Type of Babcock 
! milk-test bottle conforming 
to the requirements of the 
United States Bureau of 
Standards, and showing 
graduations. 



presence of the heavy sulphuric acid. When the solution 
of the serum solids is effected the complete separation of 
the fat and serum is accomplished by whirling in a centri- 
fuge. The fat is gradually driven into the graduated neck 
of the bottle and the percentage read directly. 

Test bottles. — The Babcock-test bottle for milk, as shown 
in figure 1, consists of a body holding about 50 cubic centi- 



meters and the neck graduated so that the percentage of 
fat may be read directly. Seventeen and one-half cubic 
centimeters are used in the test, and this volume of average 
milk weighs almost exactly 18 grams. At the temperature 
at which the bottles are standardized the specific gravity 
of butter fat is about 0.9. Two cubic centimeters weigh 
twice 0.9, or 1.8 grams, which is just one- 
tenth of the weight of the charge used in 
the test bottle. The volume between 
and 10 per cent in the neck should, there- 
fore, be 2 cubic centimeters, if the bottle 
has been correctly standardized. Each 
unit per cent is represented by a volume 
of 0.2 cubic centimeters in the neck. The 
old types of bottles were 10 per cent bot- 
tles, the smallest subdivision being 0.2 per 
cent. In the more recent types, notably 
those made to conform to the specifica- 
tions of the United States Bureau of Stand- 
ards, the necks are somewhat smaller in 
diameter and read only to 8 per cent, and 
the smallest subdivision is 0.1 per cent. 
(Fig. 2.) _ 

Milk pipette. — The charge for the Bab- 
cock test for milk is measured rather than 
weighed, the measuring instrument being 
a pipette graduated to deliver 17.5 cubic 
centimeters of milk . These pipettes, filled 
to their graduation mark, hold 17.6 cubic 
centimeters. The extra 0.1 cubic centi- 
meter is allowed for the milk which clings 
to the walls. Pipettes may be obtained 
which conform to the requirements of 
the United States Bureau of Standards. 
(Fig. 3.) 

Acid measure. — This may be either a simple glass cylinder 
graduated to deliver 17.5 cubic centimeters, or one of the 
more complicated devices shown in figures 4, 5, and 6. A 
convenient little device is the small beaker with the glass 
handle by which the proper quantity of acid may be 



Fig. 3.— Pipette 
holding 17.6 
cubic centi- 
meters, used 
in measuring 
milk in the 
Babcock test. 



8 



dipped out of a larger beaker and poured into the test 
bottle. (See fig. 7.) 

The centrifugal machine. — This is commonly called the 
Babcock tester, and various types are on the market, 
ranging from the small, two-bottle hand tester to the large 
steam turbine or electric tester, accommodating 24 or 
more bottles. (See figs. 8, 9, 10, and 11.) They all con- 
sist mainly of a horizontal revolving disk or wheel provided 
with swinging sockets to hold the bottles. At rest, these 




Fig. 4.— Simple 
acid graduate. 



Fig. 5— Burette 
for measuring 
the acid. 



Fig. 6.— A combined bottle 
and acid measure. 



sockets allow the bottles to stand upright, but when in 
motion, the centrifugal force causes the sockets to swing 
outward, bringing the bottles to a horizontal position, with 
the necks toward the center. "Where steam pressure is 
available, a steam-turbine tester is strongly recommended 
for the reason that it maintains a uniform motion under a 
definite pressure and at the same time the steam keeps 
the bottles warm and supplies the hot water required. 
Whatever kind of tester is used, it must be firmly secured 



to a rigid support. There must be no shaking or trembling 
of the tester when in motion. 

Acid. — The acid used in the Babcock test is the commer- 
cial sulphuric acid, sometimes called oil of vitriol, and 
should have a specific gravity of between 1.82 and 1.83. 
It should be kept in glass bottles or jugs, preferably with 
glass stoppers. Rubber stoppers will last for a time, but 




Fig. 7.— A dipper made entirely of glass and holding 17.5 cubic centi- 
meters for measuring acid in the Babcock test. 

the use of cork stoppers is not permissible, as cork is rapidly 
attacked by the acid. Owing to the property of sulphuric 
acid of absorbing water from the air and thus diluting 
itself, it can not be kept in open containers. 

Sulphuric acid is an extremely corrosive liquid, which 
attacks the skin, the clothing, wood, and most of the com- 




Fig. 8.— A 2-bottle hand tester. 

mon metals. Should the acid be spilled on the clothing, 
it should be immediately washed off with plenty of water, 
and ammonia water applied; this in turn must also be 
washed off. Unless the acid is washed off immediately 
after contact with the skin, severe burns will result. Acid 
spilled on the table or floor may be neutralized with wash- 
ing soda or other alkali. Lead is the only common metal 

15037°— 16 2 



10 




Fig. 9. — A hand tester for 12 bottles- 



not attacked by this acid. If much testing is to be done, 

it is a good plan to cover the testing table with sheet lead. 

Testing strength of acid. — As already mentioned, the 

specific gravity of the sulphuric acid used should be 

between 1.82 and 1.83. 
It is much better to pur- 
chase it guaranteed of the 
proper strength than to 
bother with diluting the 
stronger acid. Creamery 
supply houses handle acid 
guaranteed to be cf the 
proper strength, and if 
kept in well-stoppered 
containers it will not 
change. For the benefit 
of those who prefer to test the acid themselves, the follow- 
ing directions are given: 

Use of the acid hydrometer. — This is a hydrometer de- 
signed only for liquids having a specific gravity about 
that of concentrated sul- 
phuric acid. (See fig. 12.) 
It is standardized at 60° 
F., and for correct results 
must be used with acid at 
that temperature only. 
The acid at this tempera- 
ture is poured into the 
hydrometer cylinder and 
the hydrometer allowed to 
float in it. When it has 
come to rest, the point on 
the scale intercepting the 
surface of the acid indi- 
cates the specific gravity. 
If it is much under 1.82 
it can not be used for test- 
ing milk, and should be discarded and a fresh lot of acid 
obtained. If it is above 1.83 it may be diluted with water 
until it is of the proper strength. There are two ways of 
doing this. The acid may be exposed to the air until it 
absorbs sufficient water to lower its specific gravity; this is 




Fig. 10.— A type of steam tester 
with an arrangement for heating 
the water used in the test. 



11 

the safest and best way if the specific gravity of the acid is 
not much above the standard . The second way is to mix the 
acid with a small quantity of water. A small quantity of 
water is placed in a bottle or jar and the acid poured into 
it. Never pour water into acid, as a serious accident may 
result. After the mixture has cooled to 60° F. it is again 
tested with the hydrometer and the process repeated if 
necessary. 

DIRECTIONS FOR MAKING THE BABCOCK TEST WITH 
MILE. 

Measuring the charge. — Directions have already been 
given for preparing the sample for the test. The milk is 
poured from one beaker to another two or three times. 
The tip of the pipette is 
immediately inserted and 
the milk sucked up with 
the mouth until it reaches 
a point well above the 
graduation mark on the 
stem; the dry forefinger is 
then quickly placed over 
the mouth of the pipette. 
By slightly relaxing the 
pressure of the finger the 
milk is allowed to flow 
down until it just reaches Fig. 11.— A type of electric tester. 
the mark. The tip of 

the pipette is now placed in the neck of the test 
bottle and the milk allowed to flow slowly down the 
side. The right way is to hold the pipette obliquely 
to the mouth of the test bottle as shown in figure 13. 
The wrong way is shown in figure 14. If the bottle and 
pipette are held in the latter position the neck of the bottle 
may clog up and some of the milk run over the top. 
Care must be taken that none of the milk is lost 
during the operation. When nearly all the milk has run 
out of the pipette, the last drop is forced out with a puff of 
the breath. 

Adding the acid. — The temperature of the milk when the 
acid is added should be between 60° and 70° F., and the 
acid should be at about the same temperature. Seven- 




12 



teen and one-half cubic centimeters of the acid are meas- 
ured out, and, with the bottle held at an angle, carefully 
poured down the side, the bottle being turned slowly at 
the same time so that any milk adhering to the neck will 
be washed down. For two reasons the acid must not be 
poured into the middle of the test bottle; first, because it 
may form a plug in the neck, which may be driven out by 
the expansion of the air below; and second, because the 



r >k 




Fig. 12.— Hy- 
drometer and 
cylinder used 
in testing sul- 
phuric acid. 




Fig. 13. — The right way of add- 
ing milk to the test bottle. 
( Farrington and Woll, Testing 
Milk and Its Products.) 



acid may partially mix with the milk and produce black 
particles which do not dissolve and later interfere with 
the reading of the test. The acid and milk should now 
be in two distinct layers without much of a dark layer 
between them. 

Mixing the acid and the milk. — The acid is now mixed 
with the milk by giving a combined rotary motion and 
gentle shaking with the hand grasping the neck of the 



13 




bottle. When once commenced the mixing must not be 
interrupted until the solution is complete . The first effect 
of the acid on the milk is a curdling, which is subsequently- 
dissolved. As the solution progresses the color changes 
first to a light yellow, then to dark yellow, then through 
various shades of violet to brown and finally to dark brown, 
if the acid is of the proper strength and the milk and acid 
are at the right temperature 
when united. Too strong or 
too warm acid produces a 
dense black. If the milk has 
been preserved with formalde- 
hyde, a longer time is re- 
quired to complete the solu- 
tion, owing to the toughening 
of the casein by that preser- 
vative. Common errors of 
beginners are failure to mix 
the acid thoroughly with the 
milk and to continue the shak- 
ing until the solution is com- 
plete . A good plan is to shake 
the bottle for a minute or 
so after the solution is appar- 
ently complete. Although 
not necessary, it is preferable 
to centrifuge the bottles im- 
mediately, though they may 
be kept 24 hours if desired, 
in which case they must be 
placed in water from 170° to 
180° F. for 15 to 20 minutes 
before whirling. 

Centrifuging the bottles, — The 
bottles are now placed in 
the sockets of the centrifuge, taking care that they are 
equally distributed about the wheel or disk so that the 
equilibrium of the latter is not disturbed. An even num- 
ber of bottles should always be whirled. Should an odd 
number of tests be made a test bottle filled with water may 
be used to balance the machine. When the bottles are in 
place, the tester is covered in order to keep the bottles 



4 



/ 



\ 



Fig. 14. — The wrong way of 
adding the milk to the 
milt bottle. (Farrington 
and "Woll, Testing Milk 
and Its Products.) 



14 

from getting cold and to protect the operator from flying 
glass and acid should any of the bottles break. The tester 
is now set in motion and the bottles whirled 4 to 5 minutes 
at the proper speed. This will be sufficient to bring prac- 
tically all the fat to the surface. In cold weather, if a 
hand tester is used, it may be necessary to pour hot water 
into the jacket of the tester to keep the bottles warm. 

Speed of centrifuge. — Farririgton and Woll have calcu- 
lated the proper speed of testers with wheels of different 
diameters to be as follows: 

Revolutions 
of wheel 
Diameter of wheel in inches: per minute. 

10 1, 074 

12 980 

14 909 

16 848 

18 800 

20 759 

22 724 

24 693 

Adding the water. — With the pipette or with the device 
for the purpose attached to some steam testers, or in any 
other convenient manner, hot water is added to the bottles 
until the contents come nearly to the lower part of the 
neck. The cover is now replaced on the tester and the 
whirling repeated for one minute. Hot water is again 
added until the fat reaches a point below the highest 
graduation mark on the neck. It must never reach the top 
mark, or some of the fat may be lost. This time the water 
should be dropped directly into the fat in order to clear 
the fat of the light, flocculent material which may be 
entangled in it and which would later interfere with the 
reading of the test. The whirling is repeated for another 
minute. The temperature at which the readings are 
taken is between 130° and 140° F., and this should be 
borne in mind when the water is added, the object being to 
add the water at such a temperature that the temperature 
of the fat at the close of the last whirling will be between 
these two figures. 

The water used should preferably be soft water or con- 
densed steam. The use of hard water is liable to cause 
trouble on account of its carbonates; these are decomposed 
by the acid, liberating carbon dioxid, which may cause 



15 



6. 
c— 



foam on the top of the fat column and obscure the menis- 
cus. If soft water or condensed steam is not available, 
hard water may be used if, before heating it, a few drops of 
sulphuric acid are added. 

Reading the percentage.— -If the test has been successfully- 
conducted, the fat will be in a clear, yellowish liquid 
column sharply separated from the clear and nearly color- 
less acid solution immediately below it and with no foam 
on top. The bottles should be kept warm either in the 
tester or in warm water until read, and the 
readings should always be made at be- 
tween 130° and 140° F. The fat at this 
temperature will, if other conditions have 
been correct, have a well-defined menis- 
cus at both the top and the bottom. The 
readings are made from the extreme bot- 
tom of the lower meniscus to the extreme 
top of the upper meniscus. Figure 15 
shows this graphically. An ordinary pair 
of dividers is useful in making this read- 
ing. The points are placed at the upper 
and lower limits, then lowered until one 
point is at the mark; the other point 
will intercept the scale at the correct per- 
centage for the sample tested. 

In some steam testers where the exhaust 
steam escapes into the jacket and no ven- 
tilation is provided, the temperature of 
the bottles will be too high. In such 
case, the bottles must be allowed to cool 
to 130° to 140° F. by placing them in 
water at that temperature for several 
making the reading. 

Imperfect tests. — If the foregoing directions have been 
strictly followed, a perfect test should result. It is not to 
be expected, however, that the beginner will always meet 
with success. The next two paragraphs may be helpful in 
locating the trouble. 

An imperfect test is caused by one of three things: 
(1) Foam on the fat column obscuring the upper menis- 
cus; (2) a dark-colored fat column containing dark parti- 
cles and with dark particles obscuring the lower meniscus; 



Fig. 15.— Show- 
ing method of 
reading fat 
column in 
milk testing. 
Bead from a 
to b, not a to 
c, nor a to d. 

minutes before 



16 

(3) a light-colored fat column containing white, caseous 
material obscuring the lower meniscus. 

The first is caused by using hard water. Any one or a 
combination of the following may cause the second trou- 
ble: (a) The acid was too strong; (6) too much acid was 
used; (c) the acid was too warm when added to the milk; 
(d) the milk was too warm when the acid was added; (e) 
the acid was dropped directly into the milk; (/) the mix- 
ing of the acid and the milk was interrupted before the 
solution was complete; or (g) the acid and milk were al- 
lowed to stand too long in the test bottle before being 
mixed. The third trouble is caused by one or more of the 
following: (a) The acid was too weak; (b) too little acid 
was used; (c) the acid was too cold when added to the 
milk; (d) the milk was too cold when the acid was added; 
or (e) the mixing was not continued long enough to dis- 
solve all the serum solids. 

Tested Babcoch glassware. — Babcock-test bottles and 
pipettes should always be tested and found correct before 
being used . It is now possible to purchase test bottles and 
pipettes which have been tested and approved by the 
United States Bureau of Standards. Many States also 
have officials empowered to test and approve Babcock 
glassware. The best way is to purchase it already tested 
by the Bureau of Standards, or to have it made to conform 
to the requirements of that bureau and then tested by a 
State official. 

TESTING CREAM FOR FAT. 

While in a general way cream is tested by the Babcock 
test in much the same manner as milk, there are some 
modifications that must be observed. The range of fat in 
cream, and consequently the specific gravity is much 
greater than in milk, so that 17.5 cubic centimeters do not 
necessarily represent 18 grams, as in the case of milk. 
Cream also varies in consistency, some being thin and some 
thick; therefore. in some cases much more would adhere 
to the walls of the pipette than in others. For these rea- 
sons cream can not be accurately measured. The charge 
for the test must be weighed into the test bottle. 

Cream-test bottles. — The cream-test bottles used in the 
Babcock test are of various designs, as shown in figures 16, 
17, 18, and 19. Those conforming to the requirements of 



17 



the United States Bureau of Standards differ from milk 
bottles only in the graduations and in the length and diam- 
eter of the neck. Test bottles are made for both an 18- 
gram and a 9-gram charge. 

Cream-test balances. — Several types of balances designed 
for weighing cream charges are on the market (figs. 20, 21, 
and 22). The small torsion balances prove to be very sat- 
isfactory if care is taken that the important metal parts 



sr3o 

g-25 
g-20 

g-10 



£-5 



5^0 



g-50 
|-45 
f-40 
§-35 
§-30 
§-25 
§-20 

r is 

§-10 

1-5 
=-0 





Fig. 16.— 9-gram, 6- 
inch cream bottle. 



Fig. 17.— 18-gram 6- 
inch cream bottle. 



are not allowed to rust. Balances should be tested for 
sensitiveness from time to time and should always be kept 
in perfect condition. 

Preparing cream, for testing. — The point never to be lost 
sight of in testing cream or milk is that the small quantity 
taken for the test must be truly representative. No matter 
how carefully the test is carried out, if the charge taken 
does not accurately represent the cream or milk to be 

15037°— 16 3 



18 



^ 



=-30 



1-25 



^20 



tested, the results will be worthless. The preparation of 
cream for testing does not differ materially from that of 
milk. The fat must be evenly distributed, and if there are 
no lumps this can be accomplished by 
pouring from one receptacle to another, 
warming the cream slightly if cold. If 
lumps are present, it has been advised 
to pass the cream through a fine sieve, 
rubbing the lumps through with the 
fingers and then mixing as usual. If 
the cream has stood for some time in the 
sample jar, the top may have become 
hard, leathery, and difficult to remove. 
In this case, the jars should be set in 
warm water until the contents have 
reached 100° to 110° F., when the cream 
will be soft and can be easily removed. 
Weighing the charge. — After the sam- 
ple has become homogeneous through- 
out, the charge is quickly weighed into 
the test bottle. The weight of the 
charge depends upon the style of bottle 
used . For this purpose the 9-gram bottle 
is recommended . A pipette is useful in 
conveying the cream to the test bottle, 
as the flow can be easily controlled and 
checked on the drop when the pointer 
of the balance indicates that the correct 
quantity has been run in. This weight 
must be exact, and some experience is 
necessary before the charges can be 
quickly and accurately weighed. 

Completing the test. — Instead of add- 
ing a measured quantity of sulphuric 
acid to the cream in the test bottle, as is 
done with milk, the best way is to add the acid until the 
mixture assumes the color of coffee to which cream has 
been added. 1 The quantity of acid required to produce 
this color varies with the percentage of fat in the cream. 
If the cream and acid when mixed are about 70° F., from 

i O. F. Hunziker and H. C. Mills, Testing Cream for Butter Fat, Indi- 
ana Agricultural Experiment Station, Bui. 145. June, 1910. 




Fig. 18.— 18-gram 9- 
inch cream bottle. 



19 



9Gr 




Fig. 19. — Types of cream bottles conforming to the requirements of the 
United States Bureau of Standards. 



20 



4 to 8 cubic centimeters of acid (specific gravity 1.82 to 
1.83), depending upon the percentage of fat, will be re- 
quired for a 9-gram charge. After adding the acid to the 
cream, the procedure up to the reading of the percentage 




Fig. 20.— Type of knife-edge cream balance. 

is exactly the same as in the milk test. After the final 
whirling, the test bottles are submerged to a point above the 
fat column in water at 135° to 140° F. in a suitable tank. 
After remaining in this tank for about 15 minutes they are 




Fig. 21. — Type of torsion balance for single bottle. 

removed and the readings quickly made. The important 
difference between reading the cream test and the milk 
test is that in the cream test the fat column included is 
from the bottom of the lower meniscus to the bottom, not 
the top, of the upper meniscus. (See fig. 23.) It is advised 



21 



to destroy the upper meniscus by dropping into the bottle 
at this point a few drops of a liquid in which the fat is 
not soluble. Glymol (petrolatum liquidum, U. S. P.), 
known commercially as white mineral oil, gives satisfac- 
tory results and may be purchased at almost any drug store. 
If desired it may be colored with alkanet root. 1 If glymol 
is used, the fat column included in the reading is from the 
bottom of the lower meniscus to the line between the fat 
and the glymol. If the fat column is read with the upper 
meniscus intact, care must be taken that the eye is on a 




Fig. 22.— Type of torsion balance for several bottles. 

level with the points on the scale at which the readings 
are made; otherwise an error will be introduced. 

PRESERVING SAMPLES. 

If, for any reason, it is desired to keep a sample of milk 
or cream for a few days before testing it, a preservative 
should be added to prevent decomposition. Formalin 
(which is a 40 per cent solution of formaldehyde), corrosive 
sublimate (mercuric chlorid), or potassium bichromate 
are used for this purpose. Formalin has the advantage of 
being a liquid and easily handled; on the other hand, it 

1 Hunziker and Mills, loc. cit. 



has the property of toughening the casein and rendering it 
more difficult to dissolve later in the sulphuric acid. One 
cubic centimeter should keep a pint or a quart of milk cr 
cream for two weeks or more. Corrosive sublimate, while 
the most powerful of the three, is a deadly poison. Sam- 
ples preserved with it should be colored in some way to 
indicate the presence of the poison. Tablets of corrosive 
sublimate containing coloring matter are 
V/~v- on the market. If potassium bichromate 

is used, the samples should be kept in a 
dark place; 15 to 20 grains is sufficient 
to preserve a pint for a reasonable length 
of time. 



& 



'td 



Fig. 23— Show- 
i n g method 
of reading fat 
column in 
cream testing. 
Read from a 
toc,notato6, 
nor a to d. 



CLEANING THE TEST BOTTLES. 

After the test, and before the test bot- 
tles have become cold, they should be 
emptied with a shake or two to loosen 
the deposit of calcium sulphate which 
accumulates on the bottom. A conven- 
ient device is shown in figure 24. This 
consists of a 5 -gallon stone jar with a 
wooden cover in which one - half - inch 
holes have been bored. After the test 
the necks of the bottles are placed in the 
holes and the contents allowed to run 
out, giving each bottle an occasional 
shake. The bottles should then be rinsed 
out twice with boiling water and, after 
the outside has been rinsed off, placed 
in a suitable rack and drained. At fre- 
quent intervals the bottles should also be 
given a bath in a dilute solution of lye, 
or a solution of soap or cleansing powder. 



DETERMINATION OF TOTAL SOLIDS IN MILK. 

As brought out earlier in this circular, milk is composed 
of water and the various solids collectively known as total 
solids or milk solids. Manifestly the simplest way of 
determining the amount of total solids in a given quantity 
of milk is to separate them from the water and weigh them. 



23 



This is precisely the manner in which the total solids in 
milk are determined in the laboratory. A small quantity 
of milk is weighed into a shallow, flat-bottomed dish, and 
then heated until all the water is driven off. During this 
evaporation the milk must not be heated more than a 
degree or so above the boiling point of water, because at a 
higher temperature some of the solids are decomposed. 

Ovens.— Several types of ovens are used for holding the 
milk at the right temperature during the evaporation. 
The simplest type is perhaps the so-called double-walled 
drying oven (fig. 25) . This piece of apparatus is really one 
oven inside of another, the space between the two being 
partly filled with water. A burner placed under the oven 
boils the water, and the remaining space 
between the walls is filled with steam, 
maintaining a constant temperature in 
the inner compartment which holds the 
milk dishes. Unless carefully watched, 
the oven will "boil dry," to prevent 
which it is a good plan to attach some 
sort of condenser. The type of condenser 
known as the globe condenser is very sat- 
isfactory for this purpose. Some ovens 
are constructed with a constant-level at- 
tachment. 

Balance. — Nice weighings are required 
in the determination of total solids in milk, and it is nec- 
essary to use the type of balance known as the analytical 
balance (fig. 26), the cream-test balance not being sensi- 
tive enough for this purpose. On the other hand, the 
analytical balance can not be used with advantage in 
weighing cream charges. Both balances are required. An 
analytical balance sensitive enough for the purpose can be 
purchased for from $30 to $40. A set of accurate analytical 
weights will also be required. Space does not permit di- 
rections for using the analytical balance. If the operator 
is not familiar with its use, he is advised to consult some 
elementary treatise on quantitative chemical analysis. It 
must be borne in mind that the analytical balance is a very 
delicate instrument and should be treated accordingly. 




Fig. 24. — Jar 
with per- 
forated cover 
for use in 
emptying test 
bottles. 



24 



Desiccators. — Dishes that are warm can not be accurately 
weighed on the balance because air currents are created 
which will buoy up the scale pan sufficiently to make the 
object appear Lighter than it really is. Again, many sub- 
stances can not be exposed to the air without absorbing 
atmospheric moisture and in this way introducing an error 
into the weighing. For these reasons it is customary 
always to cool the dishes in a device known as a desiccator 
(fig. 27) before weighing them. A desiccator is a specially 




Fig. 25. — Double-walled drying oven. 

constructed covered jar containing a substance like cal- 
cium chlorid, which attracts to itself all the atmospheric 
moisture in the inclosed space surrounding it. The desic- 
cator, containing no moisture, will, of course, permit a sub- 
stance to be kept in it without absorbing any. The cal- 
cium chlorid, which forms a layer about 1 inch deep on 
the bottom of the desiccator, should be renewed as soon as 
it shows any signs of moisture. The cover of the desiccator 
should be removed only as often as is necessary, and then 
for the shortest possible time. 



25 



Milk dishes. — These are best made of aluminum and 
should be from 2 to 2 \ inches wide and about one-half inch 
deep (fig. 28). Each dish should bear a number by which 




Fig. 26. — Analytical balance. 

it can be identified; this number may be scratched or 
punched on the side. 

Preparing the dishes. — After the dishes are clean and dry 
they should be placed in the drying oven for half an hour, 
then removed and placed in the 
desiccator until cool. They 
should be handled with forceps or 
crucible tongs, and as soon as they 
are cool they are weighed on the 
analytical balance. 

Weighing the charge. — After. the 
milk has been thoroughly mixed, 
it is drawn up in a pipette and 
allowed to flow into the dish until 
a thin film just covers the bottom; 
the dish and milk are then 
quickly weighed. The weight of the empty dish sub- 
tracted from the last weight is the weight of the charge, 
and should be about 2 grams. 




Fig. 27." — Desiccator. 



26 




Fig. 28.— Milk dish. 



Evaporating the water. — The dishes containing the milk 
are now placed in the oven, dried for about four hours, and 
then placed in the desiccator until cool, when they are 
weighed. They are then returned to the oven for 30 min- 
utes, after which they are cooled and weighed as before. 

If there is no loss in weight, 
or if there is a slight gain in 
weight during the 30 
minutes, it indicates that all 
the water is driven off, and 
this last weight minus the 
weight of the empty dish is 
the weight of the total solids 
in the charge taken. This multiplied by 100 and divided 
by the weight of the charge gives the percentage. If there 
was a loss in weight during the 30 minutes, the dishes are 
returned to the oven and 
dried for another period or 
until they cease to lose 
weight. 

Determination of solids 
not fat. — The percentage 
of solids not fat, or serum 
solids, is found by sub- 
tracting the percentage of 
fat from the percentage of 
total solids. 

DETERMINATION OF 
SPECIFIC GRAVITY 
OF MILK. 

For exact work the spe- 
cific gravity of milk is de- 
termined by comparing the weight of a volume of milk with 
that of an equal volume of pure water under controlled- 
temperature conditions. For inspection work an instru- 
ment known as the Westphal balance or the special 
lactometer described in Bulletin 134 of the Bureau of Ani- 
mal Industry, United States Department of Agriculture, 
is sufficiently accurate. 




Fig. 29.— Westphal balance. 



27 



r\ 






\ 



Westphal balance. — This instrument (fig. 29) consists of 
a pivoted beam graduated on one arm and bearing a 
plummet or float. The weights in terms of specific gravity- 
represent unity, tenths, hundredths, thousandths, and 
ten-thousandths. With no weight on the beam it balances 
when the plummet floats in air. When the unit weight 
is in position, it balances when 
the plummet floats in pure water 
at the proper temperature. 
When the plummet is submerged 
in a liquid heavier than water, 
such as milk, additional weights 
are required to bring the instru- 
ment to equilibrium. The spe- 
cific gravity is read off directly 
from the value of the weights 
and their position on the beam. 
Detailed directions usually ac- 
company the instrument. 

Lactometers. — Most lactome- 
ters are not sensitive enough for 
determining the specific gravity 
of milk if more than approxi- 
mate figures are required. The 
use of either the Westphal bal- 
ance or the special lactometer, 
previously mentioned, is ad- 
vised. If, however, only ap- 
proximate results are required 
the ordinary lactometer, of 
which there are several types on 
the market, will suffice. 

The lactometer (figs. 30 and 31) 
is used exactly in the same man- 
ner as is the hydrometer in test- 
ing sulphuric acid, directions for which are given on page 
10 . Care must be taken that the milk is at the temperature 
at which the lactometer is standardized and that the lac- 
tometer floats freely in the cylinder. The specific gravity 
of milk can not be taken until the milk is three or four 
hours old . The point on the scale of the lactometer where 
the surface of the milk intercepts represents the specific 




Fig. 30.— Types of ordinary 
lactometers. 



28 



gravity which is usually expressed in 
Quevenne^ degrees. 1 A slight meniscus 
will obscure the surface line, and it is neces- 
sary to estimate its depth. This will cause 
no error if it is remembered that the point 
to be read is at the surface of the milk and 
not at the top of the meniscus. 

A type of lactometer known as the New 
York board of health lactometer is in 
somewhat general use. The scale of this 
instrument does not give the specific 
gravity directly, but is so arranged that 
milk having a specific gravity of 1.029 
(at 60° F.) will read 100°. As the zero 
mark is the point to which it will sink 
when immersed in pure water, 100° on the 
scale corresponds to 29° on the Quevenne 
scale. New York board of health lactom- 
eter degree may be converted into Que- 
venne degrees by multiplying by 0.29. 




CALCULATING TOTAL SOLIDS BY 
FORMULA. 

When the percentage of fat and the spe- 
cific gravity of the milk are known and 
only the closely approximate percentage 
of total solids is wanted, it should be cal- 
culated by the Babcock formula. The 
following table and directions for using it 
are taken from Bureau of Animal Industry 
Bulletin 134: 

1 Quevenne degrees are converted into specific 
gravity by dividing by 1,000 and then adding 1 to 
the quotient. This is done at a glance. For ex- 
ample, if the Quevenne reading is 32.5, the specific 
gravity is 1.0325. 



29 



Table for determining total solids in milk from any given , 
cific gravity and percentage of fat. 

[Per cent total solids.] 



Per- 
cent- 
age of 
fat 



Lactometer reading at 60° F. (Quevenne degrees). 



26 27 28 29 30 31 32 33 34 35 36 



2.00 
2.05 
2.10 
2.15 
2.20 
2.25 
2.30 
2.35 
2.40 
2.45 



8.90 
8.96 
9.02 
9.08 
9.14 
9.20 
9.26 
9.32 
9.38 
9.44 



9.15 
9.21 
9.27 
9.33 
9.39 
9.45 
9.51 
9.57 
9.63 



11.41 
11.47 
11.53 
11.59 
11.65 
11.71 
11.77 
11.83 
11.89 
11.95 



2.50 
2.55 
2.60 
2.65 
2.70 
2.75 
2.80 
2.85 
2.90 
2.95 



9.50 
9.56 
9.62 
9.68 
9.74 
9.80 
9.86 
9.92 
9.98 
10.04 



9.75 
9.81 
9.87 
9.93 
9.99 
10.05 
10.11 
10.17 
10.23 
10.29 



10.75 
10.81 
10.87 
10.93 
10.99 
11.05 
11.11 
11.17 
11.23 
11.30 



12.01 
12.07 
12.13 
12.19 
12.25 
12.31 
12.37 
12.43 
12.49 
12.55 



3.00 
3.05 
3.10 
3.15 
3.20 
3.25 
3.30 
3.35 
3.40 
3.45 



10.60 
10.66 
10.72 
10.78 
10.84 
10.90 
10.96 
11.03 
11.09 
11.15 



11.10 
11.17 
11.23 
11.29 
11.35 
11.41 
11.47 
11.53 
11.59 
11.65 



12.61 
12.68 
12.74 
12.80 
12.86 
12.92 
12.98 
13.04 
13.10 
13.16 



3.50 
3.55 
3.60 
3.65 
3.70 
3.75 
3.80 
3.85 
3.90 
3.95 



10.95 
11.02 
11.08 
11.14 
11.20 
11.26 
11.32 
11.38 
11.44 
11.50 



12.72 
12.78 
12.84 
12.90 
12.96 
13.02 
13.08 
13.14 
13.20 
13.26 



13.22' 
13.28 
13.34 
13.40 
13.46 
13.52 
13.58 
13.64 
13.70 
13.77 



4.00 
4.05 
4.10 
4: 15 
4.20 
4.25 
4,30 
4.35 
4.40 
4.45 



12.06 
12.12 
12.18 
12.24 
12.30 
12.36 
12.42 
12.48 
12.54 
12.60 



12.81 
12.87 
12.93 
12.99 
13.05 
13.12 
13.18 
13.24 



13.3013.55 
13.3613.61 



13.83 
13.89 
13.95 
14.01 
14.07 
14.13 
14.19 
14.25 
14.31 
14.37 



30 



Table for determining total solids in milk from any given spe- 
cific gravity and percentage of fat — Continued. 

[Per cent total solids.] 



Per- 
cent- 
age of 
fat 



Lactometer reading at 60° F. (Quevenne degrees). 



26 27 28 29 30 31 32 33 34 35 36 



4.50 

4.55 

4.60 

4.65 

4.70 

4.75 

4. 

4.85 

4. 

4.95 



12.91 
12.97 
13.03 
13.09 
13.15 
13.21 
13.27 
13.33 
13.39 
13.45 



13.92 
13.98 
14.04 
14.10 
14.16 
14.22 
14.28 
14.34 
14.40 
14.46 



14.43 
14.49 
14.55 
14.61 
14.67 
14.73 
14.79 
14.85 
14.91 
14.97 



5.00 
5.05 
5.10 
5.15 
5.20 
5.25 
5.30 
5.35 
5.40 
5.45 



13.51 
13.57 
13.63 
13? 69 
13.75 
13.81 
13.87 
13.93 
14.00 
14.08 



5.50 
5.55 
5.60 
5.65 
5.70 
5.75 
5.80 
5.85 
5.90 
5.95 



13.11 
13.17 
13.23 
13.29 
13.35 
13.41 
13.47 
13.53 
13.59 
13.65 



14.12 
14.18 
14.24 
14.30 
14.36 
14.42 
14.48 
14.54 
14.60 
14.66 



14.27 
14.33 
14.39 
14.45 
14.51 
14.57 
14.63 
14.70 
14.76 
14.82 



15.03 
15.09 
15.15 
15.21 
15.27 
15.33 
15.39 
15.45 
15.51 
15.57 



14.88 
14.94 
15.00 
15.06 
15.12 
15.18 
15.24 
15.30 
15.36 
15.42 



15.63 
15.69 
15.75 
15.81 
15.87 
15.93 
15.99 
16.06 
16.12 
16.18 



6.00 
6.05 
6.10 
6.15 
6.20 
6.25 
6.30 
6.35 
6.40 
6.45 



13.96 
14.02 
14.08 
14.14 
14.20 
14.26 
14.32 
14.38 
14.44 
14.50 



4714. 
53 14. 
5914. 
65,14. 
71 1 14. 
77:15. 
83'15. 
90' 15. 
9615. 
02115. 



14.98 
15.04 
15.10 
15.16 
15.22 
15.28 
15.34 
15.40 
15.46 
15.52 



16.24 
16.30 
16.35 
16.42 
16.48 
16.54 
16.60 
16.66 
16.72 
16.78 



6.50 
6.55 
6.60 
6.65 
6.70 
6.75 
6.80 
6.85 
6.90 
6.95 



14.82 
14.88 
14.94 
15.00 
15.06 
15.12 
15.18 
15.24 
15.30 
15.36 



15.83 
15.89 
15.95 
16.01 
16.07 
16.13 
16.19 
16.25 
16.31 
16.37 



16.84 
16.90 
16.96 
17.02 
17.08 
17.14 
17.20 
17.26 
17.32 
17.38 



31 

Table for determining total solids in milk from any given spe- 
cific gravity and percentage of fat — Continued. 

PROPORTIONAL PARTS. 





Fraction 




Fraction 




Fraction 


Lactom- 


to be 


Lactom- 


to be 


Lactom- 


to be 


eter 


added to 


eter 


added to 


eter 


added to 


fraction. 


total 


fraction. 


total 


fraction. 


total 




solids. 




solids. 




solids. 


0.1 


0.03 


0.4 


0.10 


0.7 


0.18 


.2 


.05 


.5 


.13 


.8 


.20 


.3 


.08 


.6 


.15 


.9 


.23 



Directions for using the table. — If the specific gravity as 
expressed in Quevenne degrees is a whole number, the 
percentage of total solids is found at the intersection of 
the vertical column headed by this number with the 
horizontal column corresponding to the percentage of fat. 

If the specific gravity as expressed in Quevenne degrees 
is a whole number and a decimal, the percentage of total 
solids corresponding to the whole number is first found, 
and to this is added the fraction found opposite the tenth 
under "Proportional Parts." Two examples may suffice 
for illustration: (1) Fat, 3.8 per cent; specific gravity, 32. 
Under column headed 32, 12.57 per cent is found corre- 
sponding to 3.8 per cent fat. (2) Fat, 3.8 per cent; specific 
gravity, 32.5. The percentage of total solids correspond- 
ing to this percentage of fat and a specific gravity of 32 is 
12.57. Under "Proportional Parts" the fraction 0.13 
appears opposite 0.5. This added to 12.57 makes 12.70, 
which is the desired percentage. 

An inspection of the table shows that the percentage 
of total solids increases practically at the rate of 0.25 for 
each lactometer degree and 1.2 for each per cent of fat. 
This gives rise to Babcock's simple formula: Total solids= 
\ L+1.2 F. (L=lactometer reading in Quevenne degrees 
and f=percentage of fat.) 

To illustrate the, use of the formula the following example 
is given: Fat, 4 per cent; specific gravity, 32. In this case 
one-quarter of 32 is 8; 1.2 multiplied by 4 is 4.8; 8 plus 
4.8 equals 12.8, which represents the percentage of total 
solids. 



32 

This simple formula can be used in cases not provided 
for in the table. 

DETERMINATION OF ACIDITY OF MILK AND 
CREAM. 

Acidity in milk is attributable to two causes, (1) the pres- 
ence in milk of acid phosphates and perhaps of carbon 
dioxid, and (2) lactic and other acids produced by the 
decomposition of the milk sugar by bacterial action. 
When freshly drawn milk is acid to phenolphthalein, this 
acidity is from 0.07 per cent to 0.08 per cent and is owing 
to causes given under (1). Lactic acid is not present in 
freshly drawn milk; it develops only on standing. Milk 
is not sour to the taste until it has a total acidity of at 
least 0.3 per cent. 

For convenience the total acidity of milk is usually 
calculated as lactic acid. The principle upon which the 
determination of acidity is based is the well-known 
chemical action of acids upon alkalies. To illustrate, the 
action of hydrochloric (sometimes called muriatic) acid 
on a solution of caustic soda may be taken. This acid 
has a sharp and very sour taste, while caustic-soda solu- 
tions have a soapy feel and a peculiar odor, and if suffi- 
ciently strong will attack the skin. If the solution of 
caustic soda is slowly added to the hydrochloric acid, the 
sour taste will gradually disappear until the exact point of 
neutrality is reached, when a new substance is produced — 
sodium chlorid, or common salt, which has neither the 
acid properties of the one nor the alkaline properties of 
the other. The sense of taste, however, is not sufficiently 
sensitive to determine when the exact point of neutrality 
has been reached. Phenolphthalein is an organic com- 
pound, having the property, when in solution, of turning 
pink with alkalies and remaining colorless with acids. 
Such a substance is called an indicator because it indicates 
by a color change when a certain chemical reaction has 
taken place. 

There are several so-called acid tests before the public. 
The one known as Manns' s acidity test is widely used and 
is conducted as follows: 



33 

MANNS'S ACIDITY TEST. 

Apparatus required : 
One 50 cubic centimeter glass burette graduated to 

tenths, with stopcock. 
One 50 cubic centimeter pipette. 
One 250 cubic centimeter beaker, or a white teacup. 
One support for burette. 
Glass stirring rods. 

One-tenth normal solution of caustic soda , each cubic 
centimeter of which will neutralize 0.009 gram of 
lactic acid. 
An alcoholic solution of phenolphthalein made by 
dissolving 10 grams in 300 cubic centimeters of 90 
per cent alcohol. 
One who has not had training in chemistry should not 
attempt to make the tenth-normal solution of caustic soda, 
as it can be purchased to better advantage from any 
chemical supply house. 

Conducting the test. — With the pipette 50 cubic centi- 
meters of the milk or cream is measured into the beaker or 
cup. If the cream is thick, it may be slightly warmed. 
The burette is filled with the tenth-normal caustic-soda 
solution so that the lowest part of the meniscus is level 
with the zero point on the graduations. The solution is 
now run slowly from the burette into the milk or cream, 
stirring with a glass rod at the same time. It will be 
noticed that the alkali at once produces a pink color where 
it strikes; this, however, disappears on stirring. As more 
and more of the alkali is added, it will be noticed that the 
pink color is slower in disappearing until finally it becomes 
permanent for a time. Toward the end, the alkali should 
be added drop by drop and the very first appearance of a 
permanent faint pink is the signal that the neutral point 
has been reached. This color, on account of absorption 
of carbon dioxid from the air, will disappear after standing 
a short time. The number of cubic cenlimeters of alkali 
used can be learned by referring to the burette, remember- 
ing that the reading is taken from the lowest point of the 
meniscus. 



34: 

The percentage of acidity is calculated by multiplying 

the number of cubic centimeters of alkali solution used 

by 0.009 and dividing by the number of cubic centimeters 

of milk or cream taken, the quotient being multiplied by 

100. Thus: 

-d 4- t -jv c. c. alkaliX-009 K '' nn 

Percentage of acidity = c . c , sample test ea X 100. 

If 50 cubic centimeters of the sample required 10 cubic 
centimeters of the alkali to neutralize, the percentage of 
acidity would be 

10> ^ 009 X100, or 0.18 per cent. 

THE DETECTION OF PRESERVATIVES. 

The preservatives usually met with are formaldehyde, 
borax, and boric acid, and these are not difficult to 
detect if care is used in conducting the tests. Until one 
is thoroughly familiar with the tests it is a good plan to 
run three samples together, one being the suspected 
sample, one which is known to contain the preservative 
looked for, and one known to be free from that preserva- 
tive. 

Formaldehyde. — There are two well-known tests for 
detecting formaldehyde, one known as the Hehner test 
and the other ?s the Leach test. 

In the Hehner test, about 5 cubic centimeters of the 
milk is placed in a 6 by \ inch test tube, and then about 
the same quantity of concentrated sulphuric acid to which 
a trace of ferric chlorid has been added. The acid is 
allowed to run down the side of the test tube so as not to 
mix with the milk. In a few minutes the presence of 
formaldehyde will be indicated by a violent coloration at 
the juncture of the milk and the acid. This must not be 
confused with the charring of the milk by the acid. A 
modification which avoids this charring is in use in the 
dairy laboratory of the Bureau of Chemistry, United 
States Department of Agriculture, the only difference 
being that the sulphuric acid used is diluted with water 
until it has a specific gravity of 1.8. 

The Leach test, which is the more delicate test of the 
two, is conducted as follows: To 10 cubic centimeters of 



35 

the milk in a white teacup, 10 cubic centimeters of con- 
centrated hydrochloric acid (specific gravity 1.2) contain- 
ing one part by volume of a 10 per cent ferric-chlorid 
solution per 500 parts is added and the mixture brought 
slowly to a boil over a Bunsen burner. Formaldehyde 'is 
indicated by a violent coloration varying in intensity with 
the amount present. 

Borax and boric acid. — Twenty-five cubic centimeters of 
the milk is treated with limewater until a piece of red 
litmus paper when immersed in it turns distinctly blue. 
The mixture is evaporated to dryness in a small platinum 
or porcelain dish and then burned to an ash. A few drops 
(not too much) of hydrochloric acid are added to the ash, 
and then a few drops of water. A strip of turmeric paper 
is then dipped in the solution. When the turmeric paper 
becomes dry, it will be of a cherry-red color if borax or 
boric acid is present. The test is still more certain if , 
when the paper is moistened with an alkaline solution, it 
turns a dark-olive color. 

A test for the detection of borax or boric acid which is in 
use in the dairy laboratory of the Bureau of Chemistry, 
United States Department of Agriculture, and by which 
the ignition of the milk is avoided, is conducted as follows: 
Ten cubic centimeters of the milk is mixed with 5 cubic 
centimeters of hydrochloric acid in a white cup. A strip 
of turmeric paper about 3 inches long is suspended in the 
mixture so that at least 2 inches of the dry strip remain out 
of the liquid. The dry portion of the paper will gradually 
become moist by capillarity, and if borax or boric acid is 
present the paper will take on a reddish-brown tint. If 
only a trace of the preservative is present, several hours 
may be required for this color to develop. A drop of am- 
monia water on the red portion will produce an olive- 
green color, which becomes lighter, and finally disappears 
as the ammonia evaporates. 



36 



CHEMICALS AND APPARATUS USED IN THE 
CHEMICAL ANAYLSIS OF MILK AND CREAM. 



Chemicals: 

Ammonia water. 

Borax or boric acid. 

Caustic soda. 

Caustic soda, tenth- 
normal solution. 

Caustic potash. 

Corrosive sublimate. 

Ether. 

Ferric chlorid. 

Formaldehyde. 

Hydrochloric acid, con- 
centrated. 

Potassium bichromate. 

Phenolphthalein. 

Sulphuric acid, com- 
mercial. 

Sulphuric acid, pure 
concentrated. 

Litmus paper, blue. 

Litmus paper, red. 

Turmeric paper. 
Apparatus: 

Balance, analytical , 
with weights. 

Balance, cream test. 

Balance, Westphal. 

Babcock tester. 

Beakers, 250 c. c. and 
500 c. c. 

Burner, Bunsen. 

Burette, 50 c. c, gradu- 
ated to tenths, with 
i stopcock. 



Apparatus — Continued . 

Cylinder, for acid hy- 
drometer. 

Cylinder, for lactome- 
ter. 

Condenser for oven. 

Desiccator. 

Dishes, milk. 

Dishes, evaporating, 
either porcelain or 
platinum. 

Drying oven, double- 
walled. 

Forceps. 

Hydrometer, acid. 

Jars, sample. 

Jars, stoneware. 

Lactometer. 

Measure, acid, 17.5 c. c. 

Pipette, 17.6 c. c. 

Pipette, 50 c. c. 

Stirring rods, glass. 

Support for burette. 

Test bottles, Babcock, 
for milk. 

Test bottles, Babcock, 
for cream. 

Tongs, crucible. 

Test tubes, 6 by inch. 



37 



Comparison of metric and customary weights and measures. 



Customary 

weights and 

measures. 


Equivalents in 
metric system. 


Metric 

weights and 

measures. 


Equivalents in 
customary system. 




2.54 centimeters. 
0.3048 meter. 


1 meter 


39.37 inches. 


lfoot 


1.0936 yards. 
0.155 square inch. 


1 square inch. . 


6.452 square centi- 


1 square cen- 




meters. 


timeter. 




1 square foot . . 


9.29 square deci- 


1 square met- 


10.764 square feet. 




meters. 


er. 




1 cubic inch... 


16.387 cubic centi- 


1 cubic centi- 


0.061 cubic inch. 




meters. 


meter. 




1 cubic foot . . . 


0.0283 cubic meter. 


1 cubic centi- 
meter. 


0.0338 fluid ounce. 


1 fluid ounce . . 


29.57 cubic centi- 


1 cubic deci- 


61.023 cubic inches. 




meters. 


meter. 




1 quart 


0.9464 liter. 


lliter 


1.0567 quarts. 




3.7854 liters. 


1 dekaliter . . . 


2.6417 gallons. 




64.8 milligrams. 




15.43 grains. 


1 ounce (av.).. 


28.35 grams. 


1 gram 


0.035274 ounce. 


1 pound (av.). 


0.4536 kilogram. 


1 kilogram. . . 


2.2046 pounds (av.) 



Comparison of Fahrenheit and Centigrade thermometer scales. 



Fah- 


Centi- 


Fah- 


Centi- 


Fah- 


Centi- 


heit. 


grade. 


heit. 


grade. 


heit. 


grade. 


212 


100. 00 


183 


83.89 


154 


67.78 


211 


99.44 


182 


83.33 


153 


67.22 


210 


98.89 


181 


82.78 


152 


66.67 


209 


98.33 


180 


82.22 


151 


66.11 


208 


97.78 


179 


81.67 


150 


65.55 


207 


97.22 


178 " 


81.11 


149 


65.00 


206 


96.67 


177 


80.55 


148 


64.44 


205 


96.11 


176 


80.00 


147 


63.89 


. 204 


95.55 


175 


79.44 


146 


63.33 


203 


95.00 


174 


78.89 


145 


62.78 


202 


94.44 


173 


78.33 


144 


62.22 


201 


93.89 


172 


77.78 


143 


61.67 


200 


93.33 


171 


77.22 


142 


61.11 


199 


92.78 


170 


76.67 


141 


60.55 


198 


92.22 


169 


76.11 


140 


60.00 


197 


91.67 


168 


75.55 


139 


59.44 


196 


91.11 


167 


75.00 


138 


58. 89 


195 


90.55 


166 


74.44 


137 


58.33 


194 


90.00 


165 


73.89 


136 


57.78 


193 


89. 44 


164 


72.33 


135 


57.22 


192 


88.89 


163 


72.78 


134 


56.67 


191 


88.33 


162 


71.22 


133 


56. 11 


190 


87.78 


161 


71.67 


132 


55.55 


189 


87.22 


160 


71.11 


131 


55.00 


188 


86„67 


159 


70.55 


130 


54.44 


187 


86.11 


158 


70.00 


129 


53. 89 


186 


85.55 


157 


69.44 


128 


53.33 


185 


85.00 


156 


68.89 


127 


52.78 


184 


84.44 


155 


68.33 


126 


52.22 



88 

Fahrenheit and Centigrade thermometer scales — Continued. 



Fah- 


Centi- 


Fah- 


Centi- 


Fah- 


Centi- 


ren- 
heit. 


grade. 


ren- 
heit. 


grade. 


ren- 
heit. 


grade. 


125 


51.67 


82 


27.78 


39 


3.89 


124 


51.11 


81 


27.22 


38 


3.33 


123 


50.55 


80 


26.67 


37 


2.78 


122 


50.00 


79 


26.11 


36 


2.22 


121 


49.44 


78 


25.55 


35 


1.67 


120 


48.89 


77 


25.00 


34 


1.11 


119 


48. 33 


76 


24.44 


33 


0.55 


118 


47.78 


75 


23.89 


32 


0.00 


117 


47.22 


74 


23. 33 


31 


- 0.55 


116 


46.67 


73 


22.78 


30 


- 1.11 


115 


46.11 


72 


22.22 


29 


- 1.67 


114 


45.55 


71 


2L67 


28 


- 2.22 


113 


45.00 


70 


21.11 


27 


- 2.78 


112 


44.44 


69 


20.55 


26 


- 3.33 


111 


43.89 


68 


20.00 


25 


- 3.89 


110 


43.33 


67 


19.44 


24 


- 4.44 


109 


42.78 


66 


18.89 


23 


- 5.00 


108 


42.22 


65 


18.33 


22 


- 5.55 


107 


41.67 


64 


17.78 


21 


- 6.11 


106 


41.11 


63 


17.22 


20 


- 6.67 ' 


105 


40.55 


62 


16.67 


19 


- 7.22 


104 


40.00 


61 


16.11 


-18 


- 7.78 


103 


39.44 


60 


15.55 


17 


- 8.33 


102 


38.89 


59 


15.00 


16 


- 8.89 


101 


38.33 


58 


14.44 


15 


- 9.44 


100 


37.78 


57 


13.89 


14 


-10.00 


99 


37.22 


56 


13.33 


13 


-10.55 


98 


36. 67 


55 


12.78 


12 


-11. 11 


97 


36.11 


54 


12.22 


11 


-11.67 


96 


35.55 


53 


11.67 


10 


-12.22 


95 


35.00 


52 


11.11 


9 


-12.78 


94 


34.44 


51 


10.55 


8 


-13.33 


93 


33.89 


50 


10.00 


7 


-13.89 


92 


33.33 


49 


9.44 


6 


-14. 44 


91 


32.78 


48 


8.89 


5 


-15.00 


90 


32.22 


47 


8.33 


4 


-15.55 


89 


31.67 


46 


7.78 


3 


-16. 11 


88 


31.11 


45 


7.22 


2 


-16.67 


• 87 


30.55 


44 


6.67 


1 


-17.22 


86 


30.00 


43 


6.11 





-17.78 


85 


29.44 


42 


5.55 


- 1 


-18.33 


84 


28.89 


41 


5.00 


- 2 


-18.89 


83 


28.33 


40 


4.44 


- 3 


-19. 44 



o 



'.'•'■'■.■■■" V 

.,•-■'•■•■■■■■ 

' I ' 81 " 

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